Magnetic core storage circuit



R. C. MINNICK MAGNETIC CORE STORAGE CIRCUIT 2 Sheets-Sheet 1 GENERAT/NG SYSTEM ATZORNEV' Feb. 14, 1961 Filed April 19, 1957 Feb. 14, 1961 R. c. MINNlcK MAGNETIC CORE STORAGE CIRCUIT 2 Sheets-Sheet 2 Filed April 19, 1957 /N VE N TOR l?. C. M//VN/CA' BV A T TORNEV 2,912,130. l Marcianise coRE STORAGE CIRCUIT Y 'Robert CMinnic Telephone Laboratories, Incorp N.Y., a corporation of New York Filed Apr. 19, 1957, ser. No. 653,'7'71 s claims. (c1. 340-174) orated, New Yorlr,

A type of magnetic core storage matrix well known in the art employs an Iarrangement of cores in electrical co- V incidence with a geometrical array of rows and columns. A grid of selecting Wires and a sensing wire is used to provide conductive paths for information v storage and vre t;r1eval. Each selection wire is inductively coupled -to or threaded through each of the cores in an associated row or column. The sensing wire is .threaded through l all of the cores. No two selection wires jointly thread `more than a single core. Information is read .into. a-

:designated core by pulsing with a signal ofV like vpolarity [each .of theselecting wires threading that core.' The ,strength ofA the combined signal is such that through in- Jductive coupling between the Wireandthe core, the core .i.S.-dr.iyen t0. spending to the polarity of the. signal. Retrieval of the vinformation storedin a designatedcoreis.accomplished .by again pulsing the selecting wires associated with that core. A change in the magnetic state of the core will induce no change in state, the polarity of the pulsing signal obviv ously corresponds to the direction of magnetic saturation and little or no signal is induced in the sensing wire. s One `of the major limiting factorsinstorage systems of .the type described is the' presence of disturbing. signals I on the common sensing or output wire. Although the rinterrogating pulseoccurringin-a single selection wireis `insufficient to reverse the magnetic state ofl any of the `non-selected cores on the pulse carrying wire, someshift Tin magnetic state does occur, resulting in. an induced spurious `output signal on the sensing wire. If the sensing wire is inductively coupled to each core in the same direction, these spurious signals will be additive and will Amask the signal emanating from the core being sensed. VA number of arrangements disclosed in the prior art -tend to reduce the masking effect of these spurious outlput signals. For example, by alternating the direction in which the sensing wire is coupled to each successive core, the spurious signals will alternate in polarity and -partial cancellation will occur. Another arrangement. teaches Ithreading each core with a number ofwires, no .two -wires threading more thana single core,v and applying' to each wire an equal part of the setting current desired. Inthis fashion the ratio of the output signal Ato the spurious signals is increased. Still another pro- .posal is the use of dummy cores together with biasing coils This problemis furtherdiscussed in my Patent 52,732,542, issued on January 24, 1956.

The teaching of alternating the core coupling direction `of the common sensing wire leads to the theoretical conf clusion that the total number of spurious signals, signals not canceled by others of opposite, polarity, is independ- -ent of the matrix size. For example, it can be shown, ytheoretically, that in a matrix of n x n' cores on a side, rwhere a spurious signal is designated by +1, .-1, or 0 k, Cambridge, 'Mass., 'assigner tov Bell magnetic saturation. ina direction: correan output signal in the sensing Wire. If there. is f 2,972,130 Petralia@ 141 ,195i

ice,

.according to its polarity and magnitude, the total number of unbalanced, spurious signals is in the range of i2 for even n and i4 for odd n. However, the ideal- `ization ofspun'ous signals to +1, -l or 0 is not in accord withobservation., .The total disturbance on the sutput'wire doesincrease with n. The primary reason -forthis increase is the known fact that the spurious signal produced from Ia given core storing a signal of one polarity differs from the spurious .signal from a core storing ,a signalof opposite polarity. Some degree of asymmegtry ispresent in all but an idealized hysteresis loop. Even in a hysteresis loop Ythat is ideally symmetric, the lcu-rvature of the curve at the .top .of the loop differs from that at the bottom of the loop. Consequently, a diierence can be observed between the flux change that 4occurs in each of two cores in opposite states of saturacores of identical magnetic properties. Therefore, exact -ucaincellation of spurious signals will not occur through alternating the coupling direction of the sensing wire, and

larrangements in the prior art have not been directed toward this speciiic problem.

-It is an'objecf; of this inventionto provide improved magnetic Acore circuits.

It is a more specific object of this invention to reduce t9 alminimum the spuriousbutput signals producedv by non-selected cores'in; the read-out signal of magnetic core ,circuits ;I t i s. a further object'of this invention to provide an optimum ratio in a magnetic core circuit betweenthe r eado ut signal resulting from sensing the. information L'st prcd Vin ,andesignatedlzcore .andf theY read-out signals .resulting from non-selected cores. r. 5 It a still further object of this invention to provide a read-out arrangement wherein the magnitude of spurious signals is independent of the number of cores in the matrix... These and other objects of this invention are realized with a minimum amount `of associated circuitry inY a speciiic'embodiment wherein a magnetic core matrix is L.made up of a number ofgroups of cores, each .group ,containing -a major core and a number of minor cores. -In storing a giveninformation signal, the signal is applied Y equally by means. o f major and minor selecting wires to all of the cores of Aa designated group. All 'of the cores in the group are thus driven to the same state of magnetic saturation. In a conventional array each core of the matrix' is in one or the other of the two possible states of saturation. In accordance with the principles `of the invention, each group of cores is in one vor the other of the two possible saturated states. Further, in accordance with the principles of the invention, read-out .is achieved by pulsing only the major selecting Wires. In any given group, major selecting wires thread the major A'core `and at least some of the minor cores whereas the minor selecting wires thread only the minor cores. By threading the sensing wire in accordance withea particular pattern, --to be described-in detail later herein, -substantial cancellation of spurious output signals is achieved The iinal magnitude of the sum total of the Luncanceled spurious signals is thereby made independent ofv thevvv number of cores in the matrix.

In a; second embodiment of the invention an arrange- .mentsimilar to the iirst embodiment is employed wherethe'juse of additional major wires, coupled to major Acores so that no two major wires are jointly coupled to the same core, results in an improved ratiov between the fread-outsignal and the remaining unbalanced spurious 70 .f signals.

'It is therefore one feature of thisinvention that a :magnetic core .matrixhavea number :of distinct groups Moreover, thisw variation will occur even between two -being solid and the chord broken.

integree" of cores, each group containing one major core and at least two minor cores.

lt is a further feature of this invention that va matrix A complete understanding of this invention togetherV with additional'objects and features thereof will be 'gained from consideration Yof Vthe following detailed description and accompanying drawings in which:

Fig. lV shows 'schematically a group magnetic core matrix in accordance with one specic embodiment of this invention wherein each group comprises three cores; Fig. 2 shows schematically another group magnetic .corematrix in accordance with another specific embodiment of this invention wherein each group comprises four cores;

Fig. 3 shows the relative polarities of Ithe inductive coupling between the selection .wires and the cores in a group' magnetic'core matrix illustrative of still another embodiment;

Fig. 4 shows therelative polarity of possible disturbing signals at each core in the illustrative group matrix of Fig. 3; and l Fig. 5 shows a hysteresis loop, illustrating the theory .supporting one of the principles of the invention.

Referring to Fig. 1, for the purpose of illustrating the Yprinciples of this invention, only a Y2 x 2- group matrix isrshown comprising core groups 1, 2, 3 and 4. The groupsV 'are separated, lfor purposes of identification, by dotted lines CL andv CL. Each of the four core groups comprises three cores a, b and c, each core`being'repre-- sented by a circular segment, the arc' of the' segment In each group, va represents the major core and b and c represent minor cores. Lines x1, x2, x3 and x4 and lines y1, y2, ys and y* are selecting wires. Any wire passing through a major core is amajor 'selecting'wire Any wire passing through only minor cores is a minorv selecting wire. Hence, in Fig. 1, wires x1, x3, y1 an'cl'y3 are major selecting wires .and x2, x4; y2 and y., are minor selecting wires. The line SS represents a'sen'sing wire threaded through or otherwise inductively coupled to each core in the matrix. The relative direction in which the4 sensingl wire ora selecting wire is coupled to cores in the matrix may be vdetermined by tracing any selecting wire or the sensing wire in the direction indicated by one vof the small arrows. One direction -of coupling is indicated by a wire rst intersecting a core through its dotted chord, that is to say, a wire which in coupling any particular core follows a path marked by source chord arc ground. This direction of4 coupling may be conveniently designated as the 1 direction, not to be confused with any state of magnetization, which may be similarly designated. With this convention, each of the cores of Fig. l is coupledto 'its associated pair of selecting wires in the 1 direction. Tracing the sensing wire of Fig. 1 in the direction from S toward S', it will be noted that core t a of group l is coupled in the chordarc or 1 direction andthat cores b and c of group lare coupled in the opposite direction; i.e., arcchord. This opposite direc- -tion of coupling may be conveniently designated as the 0 direction, not to be confused with any state of magor -1 according to its polarity, the total number of unbalanced spurious signals is in the range of i2 for even n and i4 for odd n.

However, in view of the fact that the spurious signal produced from a given core .storing a signal of one polarity diners from the spuriousV signal from a core storing a signal. of opposite polarity, -even where the coupling between each core land the sensing wire is in the opposite direction, i2 or i4 does not accurately represent the range of the total value of unbalanced signals. This fact may best be illustrated by referencewto the hysteresis loopvr shown in Fig'.v 5. The loop shown, having a relatively high degree of rectangularity, is representative of the magnetic characteristics of the type of core employed in magnetic storage matrices. Point P represents the magnetic state of the core storing a binary 1 and point N represents the magnetic state of the core when a binary 0 Vis stored, assuming full saturation in each case. vMinimum values of disturbing fields required to reverse the magnetic state of the core from one extreme of saturation tothe other are represented by points +Hs and -Hs. Lesser values of disturbing fields, for example those occurring in a non-selected core from interrogating pulses vin a matrix such as that shown in v Fig. 1, are represented by the points -l-hs and -hs. An

p1 are not Ythe same.

inte'rrogating pulse creating a disturbing vfield of the value ll-hs Will result in an excursion of the state of magnetization as shownby the minor hysteresis loop Pplpz if the core was'initially at point P and, Vif the core was Yinitially at` point N, the core will shift from'N to' :r3

Vand then back tov N. Similarly, `an interrogating pulse creating a disturbing eld of the value -hs' will result in an excursion of the state of magnetization as shown .by .the minor. hysteresis' loop Nnlnz, ifV the core was "variation which exists in any given core between the curvature of the top of the lhysteresis loop and .the curvature ofthe bottom of the loop. For example, the slope or curvature of the loop between points N and n3 and the slope or curvature of the loop between points P and This variation of slope' will also be observed between the top of the hysteresis loop of Vone core and the bottom of the loop of any second core even though the magnetic properties of the two cores are substantially identical. Accordingly, the true range .of the total value of unbalanced read-out signals in a matrix of the type shown by Fig. l may be more precisely indicated by the notation i(2lne) for even n an'd .1'[4-}.(nl1)e] for odd n, where e represents the uncanceled portion of spurious signals emanating from vnon-selected cores, e being greater than 0.

Vstorage is accomplished by the transmission of a pulse signal of the appropriate polarity over wires x1, x2, y1 and y2.' The strengthofthe signal transmitted is advantageously one-half that needed to saturate any given core in the l direction. Thus, regardless of the remanent Vstate of magnetic saturation in any of the cores a, b or yc Vof group 1 before the selecting wires were energized,

Vat .the conclusion of the energizing signal each of the -'cores will be driven to magnetic. saturation in the 1 direction.v .The'sto'rage ofthe information bit will acco'rdingly have been made in all of the cores of a group 'rather than `in a single'core .as would vhave been the case in aconventional n x-n magnetic core array where 'groups of cores are not employed.

It should also be noted that in the process of storing the information bit the only cores driven to saturation in the desired direction were the cores in the designated group 1. This was achieved without the aid of any biasing arrangementl but instead was accomplished by the input signal itself. Accordingly, during normal operation, all of the cores in any designated group in the matrix are at one or the other of the two possible states of saturation. The half strength signals transmitted along x1, x2 and y1, y2 were of course insuiiicent to reverse the state of saturation existing in the cores of group 2 and group 3. 'I'he only points at whichv two energized wires combined to create a full strength signal were at cores a, b and c of group 1. l

Let us now assume that the interrogation of group 1 is desired in order to produce a read-outsignal. This step is accomplished by pulsing major selecting wires x1 and y1 only. If the polarity of the interrogating signal is opposite to Ithat of the stored information bit it is apparent that the state of magnetic saturation in core a of group 1 will be reversed. A full output signal will be induced in selection wire SS. At the same time, small spurious signals will be induced in the sensing wire at cores b and c of group 1 as a result of the slight shift in magnetic state created by the half amplitude interrogating signal received by core b through x1 and by core c through y1. Since the direction in which the sensing wire is coupled to cores b and c of group 1 is opposite to the sensing' wire coupling direction at core a, the polarity. of these spurious signals will be opposite `to that induced at core a. Cancellation between the spurious signals will'not occur; instead, the disturbances will be additive..

It can readily be seen that spurious signals will also be introduced on the sensing wire SS by the interrogating pulse in selection wires x1 and y1 at cores a and c of group 3 and at cores a and b of group 2. The direction of inductive coupling between the sensing wire and core a of group 2 is opposite to the direction of inductive coupling of the sensing wire to core b of group 2. Thus, cancellation of .these spurious signals will occur. 'I'his same cancellation might have taken place in a conventional n x n matrix if the magnetic states of cores a and b of group 2 were the same prior to the interrogating signal. Obviously, such a condition would always be a matter of chance. In accordance with the principles of the invention, however, cores a and b of group 2 will always be in the same magnetic state of saturation, i.e., at one extreme state or the other. The cancellation of spurious signals which takes place is therefore an exact cancellation and will not be eiected by the asymmetry of the hysteresis loops or by loop curvature differences. The same complete cancellation of spurious signals which occurred between'cores a and b of group 2 will also occur between cores a and c of group 3. The cores of group 4 are of course not involved in the production of spurious signals inasmuch as they were in no way affected by the interrogating signal. It is evident then that the range of spurious output signals in an n x n matrix constructed and operated in accordance with the principles of the invention is i2 for even values of n and is completely independent of n. It can of course be shown in the same manner that the range of spurious lsignals for odd values of n is i4.

It will be recalled that one of the feature of the invention disclosed in connection withthe operation of the matrix of Fig. 1, was that in any single core group all of the cores are driven to the same polarity of satura- .t .iP wir?, Caudina. Interesados af a .maior wie.

case, the requisite condition of having all of the cores of any selected group saturated in `the same direction will not exist until a new storage is eiected in that group. It will be apparent to those skilled in the art, however, that pulse generating' circuitry responsive to read-out signals from the matrix may be employed advantageously to restore any signal after interrogation has taken place. Such restoring circuitry is known in the art and may comprise other magnetic core matrices, pulse generating electron tube circuitry or other similai arrangements.-

Consideration of further embodiments of the prin: ciples of the invention will be aided by reference to certain terms and notations which may conveniently be employed to designate the relative directions in which tio'n when a signal Yis stored.v It will be recalled further the selecting wires and the sensing wire lare coupled to the cores of a magnetic core matrix. As noted above herein, all of the cores of the matrix shown in Fig. 1 are coupled to their associated selecting wires in the same direction; i.e., the chord arc or 1 direction, while the sensing wire is coupled to some of the cores in the 1 direction and to others in the 0 direction. We can conveniently and graphically depict these relative wire-tocore coupling directions by arrays of Os `and ls, the numerals beingso disposed that each is placed in the same relative position as the core it represents.l Consequently, for the matrix of Fig. 1, the selecting wire core coupling array, termed selection array, or S array, may be shown as follows: 1

Similarly, the sensing wire-to-core coupling array, @it veniently termed sensing array or Q array, may-be shown as follows:

The dotted lines of the Q array (2) are helpful in defining still another term of interest which may be employed to designate one of the features of a magnetic core matrix, arranged in accordance with the invention. If in a Q array each lower-left-to-upper-right diagonal that joins diagonally adjacent core coupling designators defines a line of all Os or all ls, it is said to have threading property. Accordingly, it is apparent that the Q array (2) defining the core matrix of Fig. 1 has threading property.

Further examination of the S array (l) andthe `array (2) of the Fig. l matrix shows that in any palticular Acore group, the polarity of possible output signals from the minor cores is opposite to the polarity of a simultaneous output signal from the major core of that group. For example, the major or a core of group l is coupled to Vthe selecting wires and also to the sensing wire in the 1 direction. While the minor cores b and c are also coupledto the selecting wiresin thev 1 direction, they are coupled to the sensing wire in the oppositoorf) direction. Obviously the same result would be attained in a matrix in which the relative coupling directions of uw Sensing andrselctins .wires were Opposite wtthare- 7 spect to any particular major core and the same. with respect to the associated minor cores.

AThese core coupling relationships may be more readily defined by an array of s and ls, similar tothe S and Q arrays, where a 1 indicates that the represented core is coupled to the sensing and selecting wires in the same directionl and where a 0 indicates opposite coupling directions' as between selecting wires and the sensingwire. Such an array is thus a consequence of both the S and Q arrays and it is descriptively designated product array, or P array; The P array of Fig. 1 appearsV as follows: A

`The dotted lines of the P array (3), which correspond to the major selecting wires of Fig. l, are useful in dening an additional term which may conveniently be employed to describe a magnetic core matrix in accordance with the invention. Every P array that has 1 designators and 0 designators in equal numbers along each major selecting Wire in every core group and such designators in unequal numbers along each minor selecting wire in every core group is said to have cancellation property. Evidently then, the matrix of Fig. 1 is further defined by a P array with cancellation property.

Since in the example above all of the cores are coupled to the selecting wires in the same direction, as indicated by the fact that all t'ne elements of the S array are of the same value, in this case 1, the P array (3) takes the same form as the Q array (2). It is to be understood, however, that the principles of the invention are equally applicable to arrangements in which the selecting wires couple some of the cores in one direction and other cores in the opposite direction.

1t should also be noted that a uniform row 4and column disposition of core elements is not signicant insofar as the principles of the invention are concerned. Uniform arrangements, as shown herein, readily illustrate the principles of the invention, but a random core disposition should serve equally Well as an embodiment of the features of the invention.

Another term which is helpful in defining the characteristics of core matrices in accordance with the invention is input selection ratio, pi, which is used to indicate the number of major selecting wires employed for storage input in -a single group. For example, for the matrix of Fig. 1, p1=2. A similar term, output selection ratio, po, indicates the number of major selecting wires used for the interrogation of a single core group. For example, for the matrix of Fig. l, 120:2.

VThe principles illustrated thus far can be extended to vmatrix systems having output selection ratios of po 2. For example, Fig. 2 shows schematically a 2 x 2 group matrix in which p0=3. Four groups l, 2, 3 and 4 of cores a, b, c and d are employed andare separated for 'identification by dotted lines CL and CL. Notations for major and minor selection wires and for the sensing Awire are the same as used for Fig. 1 with the exception of the employment of additionalfrnajor selection wires yzl and z2. To store an information bit in this matrix, fior example in core group l, wires x1, x2, y1 and y2 are energized. The selection ratio for reading in is thus 'pr- 2; To read outv of'core group 1, major selection 11 1,1 o0 11 o0 1 1 S- A Q (n 111,1 11 oo 1,1 oo

It will be noted that the matrix deiines a Q array with the threading property and a P array with the cancellation property.

While it has been stated that the cancellation of spurious signals in magnetic arrays constructed and op erated in accordance with the principles of the invention is exact, it is still desirable, particularly in the case of larger matrices, to increase the value of theoutput selection ratio, in the manner illustrated by the matrix of Fig. 2, as the problem of reading information into a magnetic matrix is considerably less critical than that of reading information out. Accordingly, an advantageous arrangement is to maintain the input selection ratio at a value of 2l and to increase the output selection ratio. Such an arrangement will overcome the possible masking eiiect of relatively minute spurious signals which may be caused by variations iny magnetic properties among individual cores in the matrix or by spurious signals induced from outside sources. In this connection it should be noted that the relatively minute spurious signals which may resultl from a-'variance in magnetic properties among cores are to be distinguished from the spurious signals resulting from cores of identical magnetic properties wherein the stored signals are of opposite polarity. The latter spurious signals are not present, i.e., exact cancellation occurs, in a matrix constructed and operated in accordance with the principles of the invention.

In order to obtain higher output selection ratios the size of the core group must be increased. An illustration is provided by Fig. 3 showing a selection array and by Fig. 4Vwhich is both the product and output array of a 3 x 3 group matrix with an input selection ratio of 2 and an output selection ratio of 4. The four selection wires in such a matrix may be defined as (0, l), (1,10), (l, -1) and (2, 1) where the paired numbers give respectivelyV thev horizontal and vertical distance modulo n betweencores on the same wire. In the case of the matrix illustratedby the arrays of Fig. 3 and Fig. 4, it will be noted that there are three cores, or a total of seven, added' to each core group over those n eededk for the case illustrated by Fig. 2 in which the output selection ratio was 3. Each core group in the Fig 3, Fig. 4 example is based on a 5 x 5 matrix. If an n x n matrix contains m x m core groups it can be shown that the output selection ratio is restricted by mu-I-l posmaller of (5) where m0 and n0 are the, least prime factors of m andl n, respectively.`

It is to be understood that the above-.described yan rangements are illustrative of the application of the principles of this invention. -Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

l. In combination, in an information storage system, an even plurality of magnetic cores arranged in a matrix of core groups, each comprising an equal number' of at leastv three of said cores, each of said cores being characterized by a substantially rectangular hysteresis loop and by the capability of attaining'eitherof two stable states of magnetic remanence, means including a plurality of selecting wires, each inductively coupled in a single direction to preassigned ones of said cores, for storing a single information bit in all the cores of any designated one of said groups, means including a selecting wire, said selecting wire being coupled .to one half the number of said cores in said single direction and to the other half of said cores in the opposite direction, for reading out said infomation bit from a single core f said designated group, and means for limiting the magnitude of spurious signals, impressed on said sensing wires during the operation of said reading-out means by cores other than said single core, to a level which is independent of the total number of cores in said matrix, said limiting means comprising a preassigned order of relative coupling directions between said sensing Wire and said cores, said order being characterized by threading property in the Q array of said matrix and by cancellation property in the P array of said matrix.

2. In an information storage system, in combination, a matrix of magnetic cores, each characterized by a substantially rectangular hysteresis loop and by the capability of attaining either of two stable states of magnetic remanence, a plurality of major selecting wires, a plurality of minor selecting wires, and a sensing wire,- said matrix comprising, a plurality of core groups each including a major core inductiveiy coupled to a respective unique pair of said major selecting wires only and to said sensing wire, and two minor cores each inductively coupled to only one of said major wires, to only one of said minor wires, and to said sensing wire, means for simultaneously applying electrical pulses to all of the major and minor selecting wires coupling the cores of any selected one of said groups, thereby to store a single information bit in said selected group, means for simultaneously applying electrical pulses to any designated pair of major selecting wires jointly coupling a designated major core, thereby to impress a read-out signal on said sensing wire, and means for limiting the total magnitude of spurious read-out signals impressed on said sensing wire by all of the cores, other than said designated major core, which are coupled by said designated major selecting wires, said limiting means comprising a preassigned order of relative coupling directions between said selecting wires and said cores and between said sensing wire and said cores, said order defining a Q array with threading property and a P array with cancellation property.

3. In an information storage system, in combination, a matrix of magnetic cores each characterized by a substantially rectangular hysteresis loop and by the capability of attaining either of two stable states of magnetic remanence, a plurality of major selecting wires, a plurality of minor selecting wires, and a sensing wire, said matrix comprising a plurality of core groups each including a major core inductively coupled to a unique three of said major selecting wires and to said sensing wire and three minor cores each inductively coupled to a respective one of said major wires, to not more than two of said minor wires and to said sensing wire, means for simultaneously applying electrical pulses to the major and minor selecting wires coupling the cores of any selected one of said groups, thereby to store a single information bit in said selected group, means for simultaneously applying electrical pulses to any designated three of said major selecting wires jointly coupling a designated major core, thereby to impress a read-out signal on said sensing wire, and means for limiting the total magnitude of spurious signals impressed on said sensing wire by all of the cores, other than said designated major core, which are coupled by said designated major selecting wires, said limiting means comprising a preassigned order of relative coupling directions between said selecting wires and said cores and between said sensing wire and said cores,'said order being characterized by threading property in the Q array of said matrix and by cancellation property in the P array of said matrix.

4. An information storage system comprising, a matrix of n x n magnetic Acores each characterized by a substantially rectangular hysteresis loop and by the capa'- bility of attaining either of two stable states of magnetic remanence, at least four major selecting wires, at least four minor selecting wires, and a sensing wire, said matrix comprising at least four groups of said cores, each group comprising an equal number of cores including one major core and at least two minor cores, each major core being inductiveiy coupled, uniquely, to at least two major selecting wires, and each minor core being inductively coupled, uniquely, to one major selecting wire and at least one minor selecting wire, means for simultaneously applying an electrical signal to all of the major and minor selecting wires coupled to the cores of any designated one of said groups, thereby to store the same signal in all the cores of said designated group, means for simultaneously applying an electrical signal to all of the major selecting wires jointly coupling any designated one of said major cores, whereby a readout signal from said designated major core and a spurious signal from each of the other cores coupled by said last named major selecting wires are impressed on said sensing wire, and means for limiting the total magnitude of said spurious signals to a level which is independent of n, said limiting means comprising a preassigned order of relative coupling directions between said selecting wires and said cores and between said sensing wire and said cores, said preassigned order being characterized by a Q array with threading property and `a l array with cancellation property.

5. Apparatus in accordance with claim 4 wherein each of said signal applying means includes a respective pulse generator.

References Cited in the le of this patent UNITED STATES PATENTS 2,691,154 Rajchman Oct. 5, 1954 2,856,596 Miller Oct. 14, 1958 2,881,414 Haynes Apr. 7, 1959 

